The present invention relates to a lens whose at least one lens surface is a convex surface. Particularly, the present invention relates to a shape of a lens that is suitable for coating.
In general, a lens surface is covered with a protective coating that prevents a scratch (for example, see Japanese patent publication No. P2000-210614A).
A procedure to apply this kind of coating is as follows.    (1) Hung a lens so that the optical axis keeps level.    (2) Immerse the lens into a solution of coating material and leave the lens in the solution for a predetermined period.    (3) Pull up the lens from the solution at a predetermined pulling-up speed.    (4) Cure the solution adhered to the lens surface by predetermined curing methods (heating or irradiating ultraviolet rays).
However, an application of the above-described coating to a lens having a flange, which is formed around the lens to be projected in a radial direction perpendicular to an optical axis and to be continued from a convex surface, causes the following problem.
That is, the solution collects at a lower area of the convex surface inside the flange by influence of gravity when the lens is pulled up from the solution after the immersion in the solution. The collection of the solution is referred to as “a puddle” in the following description.
Since a puddle remains after the curing, the thickness of the coating, which should become uniform, increases only in the lower area due to the puddle. This partially changes refractive power of the lens, which distorts an image when the lens is applied to an imaging optical system, for example.